Overlays have become commonly employed in next generation switching architectures to solve problems relating to Layer 2 (“L2”) multipathing, L2 topology convergence, seamless mobility, and L2 extensions across IP cores. One downside to using an overlay (especially in the case of an IP based overlay) is resultant excessive network bandwidth usage due to the additional headers and degradation in hardware switching performance.
For example, the header over may be around 20% for Internet Mix (“IMIX”) sized packets used in an IP based overlay such as Locator/ID Separation Protocol (“LISP”) or other virtual LAN (vLAN) environments. Hardware performance degradation may be due to additional passes through the forwarding pipeline for overlay encapsulation and decapsulation processing.
On the decapsulation side, for an IP overlay, the pipeline resources to perform IP Source lookups on the outer header will require one forwarding pass through most of the forwarding pipelines to ensure IP packet header integrity and determine outer header decapsulation criteria. On the encapsulation side, one pass may be required to add the encapsulation header. A second pass may then be needed to bridge (route) the frame based on the outer encapsulation header.
When multiple overlay protocols are involved for the same frame in a single node, both the decapsulation and encapsulation overheads are added. For example, an incoming Layer 3 (“L3”) LISP frame may go first through a decapsulation operation and subsequently go through a L3 and L2 forwarding lookups. The L3 LISP frame may then be encapsulated into a L2 LISP frame in an outgoing virtual vLAN.
There exists a need to take advantage of certain network topologies to decrease the level of overhead in such scenarios.